1. Field of the Invention
The present invention relates to a control method/system for controlling the operation of electrically actuated shifting mechanisms such as, for example, electrically actuated X-Y shifting mechanisms for automated mechanical transmissions. In particular, the present invention relates to controls for electrically actuated shifting mechanisms which are effective to periodically relieve trapped frictional force in the shifting mechanisms.
2. Description of the Prior Art
Automated mechanical transmission systems utilizing shifting mechanisms controlled by command output signals from a system controller are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 5,050,427 and 5,053,959, the disclosures of which are incorporated herein by reference. Such fully and partially automated systems are based on mechanical transmissions utilizing positive jaw clutches, which may or may not be synchronized, to selectively engage and disengage selected ratio gears, as seen in U.S. Pat. Nos. 4,754,665; 4,920,815 and 5,000,060, the disclosures of which are incorporated herein by reference.
Shifting mechanisms having a shift member, such as a shift finger or the like, movable along a single axis or along two perpendicular axes by the selective actuation of one or more electric motors also are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,873,881 and 5,219,319. In such devices, the direction of rotation and/or the output torque of the electric motors, typically bidirectional DC motors, is a function of the polarity and/or amperage of the current applied to the motor.
While the prior art electric motor-actuated shifting mechanisms are generally satisfactory, they are subject to improvement, as the controls therefor typically stepped the motors immediately to and maintained the motors at the full target current, which often resulted in overshooting the intended force when a stop is encountered and did not provide for relieving the resultant trapped frictional forces.